1. Technical Field
The invention is related to the field of air bearing sliders for use in magnetic head assemblies.
2. Background
Computer disk drives store and retrieve data by using a magnetic head positioned close to a rotating disk with some magnetic material at or near its surface. The head operates to either write data onto the disk by aligning magnetic poles of the magnetic material or read data by sensing the alignment of the poles. Because the magnetic fields are relatively small, it is of critical importance that the head is kept very near the disk surface. Not only does this improve the writing and reading of data, but the closer the head can be placed, the greater the storage capacity of the disk can be.
In order to position magnetic heads at acceptable distances above the surface of disks, heads are typically mounted to air bearing sliders. An air bearing slider is a device which is specifically shaped so that when placed into the airstream existing close to the surface of a rotating disk, the slider will provide a lifting force to cause it to fly above the disk. As magnetic heads are normally much smaller than sliders, they can be mounted to sliders and flown with the slider above the disk. Flying the magnetic head by way of a slider allows the distance between the head and the disk surface to be kept relatively small and constant.
Usually, the slider and magnetic head assembly is bonded to an actuator arm which allows the slider to maintain a desired position relative to the disk surface. The actuator arm also enables reciprocation of the slider across the disk surface to precise positions over individual data tracks of the disk.
Usually, the slider will be in a pitched up attitude when it is flying. This attitude assists the slider to create a lifting force. Because the pitched up attitude places the trailing edge of the slider closest to the surface of the disk, the trailing edge is the desired location for placement of the magnetic head, which provides increased performance the closer it is kept to the disk surface.
Generally, as the airflow is increased, the slider will produce greater lift and thus raise to a higher position above the disk surface. This causes the slider to vary its height as its location along the radius of the disk is changed. The closer to the center of the disk the slower the airflow, lower the lift and thus the lower the slider will fly. The closer to the outer edge the slider is, the faster the airflow, greater the lift and the higher the slider will fly. However, changes in flying height are undesirable as a more constant flying height would allow the magnetic head to be positioned closer to the disk surface regardless of its radial location above the disk.
Of course, just as the slider can take-off, it also can land.
When the disk is at rest, the slider and the disk are in contact. Upon startup, the friction force required to separate the slider and disk is referred to as "stiction". By causing a certain amount of torque on the disk, stiction can damage, or at the very least reduce the life of the disk motor. High stiction may cause the disk to not be able to begin turning and even if it can rotate the disk may not be capable of obtaining high enough rotation to allow the slider to take-off.
The `skew angle` is the angle between the direction of the disk's tangential velocity (airflow) and the slider's longitudinal direction. Typically, a disk drive can have either a linear or a rotary actuator. With linear actuators the slider has little to no skew angle. With disk drives becoming more compact, manufactures have moved to using rotary actuators. With a rotary actuator the slider is mounted along a rotary arm. With a rotary actuator, the orientation (skew angle) of the slider with respect to the disk changes continuously. Generally, rotary actuators have skew angles of roughly .+-.12-13 degrees.
Variations in skew angle lead to variations in lift and therefore flying height. It is desired that sliders used with a rotary actuators be able to operate over a wide range of skew angles with a minimal variations to the flight height.
Flight height is also affected by other factors. For instance, significant pitching and/or rolling of the slider will adversely affect the flying height. Usually, as the slider pitches upward, the lift will increase and the slider will fly higher. Pitching down will have the opposite effect and decrease the flying height. The more variation in pitch, the less constant the flying height will be. Pitching can however be reduced by increasing the pitch stiffness of the slider. Likewise, increasing the roll stiffness will provide a more constant flying height as it will prevent the sides of the slider from dropping to close to the disk surface.
Variations in the loading of the slider will also affect the flying height. If the load is increased, then the slider will fly lower or will have to produce a greater lift force to maintain the same height. The degree to which the flying height will be affected by variations is loading is referred to as load sensitivity. A high vertical stiffness of the slider will provide a lower load sensitivity.
Many prior sliders have been designed with features intended to help maintain a more constant slider flying height. These devices have had varying degrees of success.
One of the early sliders is the 3370 thin film head slider of the IBM 3370 disk drive. FIG. 1 shows an example of a 3370 slider. This slider is a two rail taper-flat design supported by a leaf spring suspension. The read-write head is located at the trailing edge of each rail, such that with the slider pitched up relative to the surface of the disk, the read-write head is positioned close to the disk surface. For disk drives which used smaller disks, and therefore lower airflow velocities, the distance between the rails would be made wider to provide greater lift. Other modifications on this basic slider design included variations to the shape of the rails. For example, IBM produced the 3380K slider where each side rail had a widened leading edge rail that flared down to a smaller rail width towards the trailing edge.
Other prior sliders included those used for low-end applications having heads comprising a magnetic ring core and wound coil. These sliders included two types, the minimonolithic and the minicomposite. The minimonolithic slider was a tri-rail design. A taper-flat bearing area was provided by the outer two rails of the design. The center rail defined the width of the magnetic head located in the trailing edge. Although about the same size as the minimonolithic slider, the minicomposite slider lacked a sizable depression, or depressions, in the area between the rails as existed with the other designs.
One problem with these types of sliders was that as the slider traveled further outward on the disk, the increased airflow would produce greater lift and would cause the slider to fly progressively higher. This caused a direct decrease to the performance of the magnetic head. Further, because these designs had a very simple lifting mechanism, the sliders had low vertical and pitch stiffnesses. Also, the flat rails produced relatively high stiction values. When used with rotary actuators, these designs tended to be highly affected by the skew angles and performed poorly. The result was that these prior designs could not provide the nearly constant low flying height and stiffness required by the increasing data capacity requirements of modern disk drives.
Thus, a slider is sought which will maintain a low and nearly constant flying height and low stiction. To do so, the slider must have a low sensitivity to changes in airstream velocity. The slider must have a low skew sensitivity so that it can operate on a rotary actuator over the entire disk surface with little variation in the flying height. The slider must have an vertical stiffness great enough to minimize load sensitivity and possess pitch and roll stiffnesses high enough to minimize unwanted pitches and rolls. Of key importance is that the slider be configured to have reduced stiction values.